Arrangement for measuring and cancelling bias distortion in binary signals of the type not comprising any zero-frequency spectral components

Abstract

An arrangement for measuring and cancelling bias distortion is designed for correcting the distortion of the binary signals which do not comprise any zero-frequency spectral components, automatically and cyclically measures said distoration (DM) by consecutive analyses of the binary data at a sampling frequency (SCK) which is a multiple of the data frequency in order to determine the sign and the quantized value of the distortion (UDC). It includes distortion cancelling means (CC) which augment the length of the binary elements selectively as a function of the sign of the distortion and proportionally to the quantized value of the said distortion and this is done until the distortion is cancelled completely.

I claim: 
     
       1. An apparatus for cancelling bias distortion in an input binary signal having first and second binary states and a predetermined data rate, said binary signal being of the type having no zero frequency spectral components when free of bias distortion, which bias distortion when in a first direction increases each duration of the first binary state and when in a second direction increases each duration of the second binary state by producing an output binary signal which corresponds to said input binary signal but with said bias distortion substantially cancelled, said apparatus comprising: input means for said input binary signal;   output means for said output binary signal;   correcting circuit means for correcting for bias distortion, having an input fed by said input means and having an output feeding said output means, said correcting circuit means comprising means for augmenting each duration of one of said binary states in agreement with a bias distortion sign control input to said correcting circuit means, in an amount in proportion to a quantized distortion value control input to said correcting circuit means;   bias distortion sign control input forming means fed by the output of said correcting circuit means for sampling said output binary signal at a sampling frequency which is a predetermined multiple of said data rate and, based on the number of occurrences of a predetermined one of said binary states in a predetermined number of sequential samples corresponding to a preset measuring time period, forming said bias distortion sign control input as indicative of a direction of bias distortion determined in each measuring time period; and   means for forming said quantized distortion value control input by adjusting a quantized measure of the bias distortion as a function of the said direction of bias distortion determined in each measuring time period.   
     
     
       2. The apparatus as claimed in claim 1 wherein said bias distortion sign control input forming means comprises a distortion measuring circuit and wherein said means for forming said quantized distortion value control input comprises an up/down counter whose counting direction is controlled by said bias distortion sign control input and whose count comprises said quantized measure. 
     
     
       3. The apparatus as claimed in claim 2 wherein said distortion measuring circuit comprises means for determining whether said predetermined one of said binary states occurs in more than half of said predetermined number of samples. 
     
     
       4. The apparatus as claimed in claim 3 wherein said bias distortion sign control input forming means further comprises a time base means for counting at the sampling frequency to measure the preset measuring time period and for generating a reset signal at the end of each said preset time period; and wherein said distortion measuring circuit comprises a counting means, whose count is reset in response to said reset signal, for counting the number of occurrences of said predetermined one of said binary states in sequential samples of said output binary signal within each preset measuring time period. 
     
     
       5. The apparatus as claimed in claim 1 wherein said correcting circuit means comprises a variable duration monostable circuit formed by a counter means for counting a number of counts determined by said quantized distortion control input in response to a state transition in said input binary signal in a state transition direction corresponding to said bias distortion sign control input. 
     
     
       6. The apparatus as claimed in claim 2 wherein said correcting circuit means comprises a variable duration monostable circuit formed by a counter means for counting a number of counts determined by said quantized distortion control input in response to a state transition in said input binary signal in a state transition direction corresponding to said bias distortion sign control input. 
     
     
       7. The apparatus as claimed in claim 3 wherein said correcting circuit means comprises a variable duration monostable circuit formed by a counter means for counting a number of counts determined by said quantized distortion control input in response to a state transition in said input binary signal in a state transition direction corresponding to said bias distortion sign control input. 
     
     
       8. The apparatus as claimed in claim 4 wherein said correcting circuit means comprises a variable duration monostable circuit formed by a counter means for counting a number of counts determined by said quantized distortion control input in response to a state transition in said input binary signal in a state transition direction corresponding to said bias distortion sign control input.